The relationship among organic matter and specific surface in a soil

FILGUEIRA ROBERTO R; SARLI GUILLERMO O.; GELATI PABLO R.; SORACCO C. GERMÁN; LOZANO LUIS A.; ARNAL PABLO

Conferencia; HK 2010 - Humboldt Kolleg International Conference on Physics Argentina-Alemania: un siglo de cooperación científica en Física; 2011

The specific surface area (SSA) of soil organic matter (OM) has been worldwide considered to range from 500 to 800 m2 g-1, based on data of ethylene glycol (EG) retention before and after the removal of OM of soil samples with H2O2. However, measurements with the Brunauer, Emmett and Teller method (BET), using N2 adsorption at 77 K, resulted in values of SSA for OM two order of magnitude smaller than the former ones. It was apparent that an overestimation of the effect of MO on SSA resulted when polar solvents were used. Some authors reported a positive relationship between the soil OM content and the SSA, but large amounts of OM in soil resulted, after other authors, in reduced SSA when the BET method was used. With the objective to contribute to a better knowledge about the OM role in edaphological processes, determinations of SSA in samples from a Typic argiudoll with different OM contents and constant clay contents (around 20%) were made. Measurements were carried out with N2 at 77 K, and the isotherms were interpreted with the BET model. Destruction of OM with H2O2 increased SSA in all cases. Values of OM content ranged from 2.8 to 11.5 %. Values of SSA ranged from 7 to 18 m2 g-1. Results showed a negative non linear relationship between SSA and the OM content of the samples. The increments in SSA, normalized by the content of removed OM, suggested that the adsorption of MO on the mineral surface is not uniform.